Method and device to determine delivery rate or mass flow rate of material conveyed by a high density liquid piston pump

ABSTRACT

The invention relates to a device and a method to determine the delivery rate or mass flow rate of material conveyed by a high density liquid piston pump ( 10 ) through a delivery line ( 24 ). The exact determination of the above mentioned variables is achieved by mounting the delivery cylinder ( 1 ) in a housing ( 30 ) with radial and axial slack and suspending it on at least one weighing cell ( 36 ) forming one piece with the housing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a device for determining the delivery rate or themass flow rate of a material conveyed through a delivery conduit by ahigh-density liquid piston pump comprising at least a conveyancecylinder and a conveyance piston. During a filling stroke (suctionstroke) the conveyance cylinder is filled with a material from amaterial providing container, and during a pressure stroke, withdisplacement, the material is emptied into the delivery conduit.

2. Description of the Related Art

Principally with high-density pumps, which are incorporated into aprocess engineering or engineering chemistry process, there is arequirement to measure and document the mass flow rate and to use thismeasured value in certain cases as the control value or set value forplant units or equipment situated upstream or downstream or and toincorporate this in a feed back system. This is the case for example inthe conveyance of sewage sludge for the incineration of sewage sludge.

Volumetric flow meters in the form of cams-counters for Newtonian fluidsare known, which are built into the delivery conduit as “motor” and inwhich a volume wheel is caused to rotate as a consequence of the pumpingprocess. The revolutions of the volume wheel are added via an impulsedisk and converted into volumetric flow in an evaluation unit on thebasis of the known displacement volume.

Further, it is known in the case of two-cylinder high-density fluidpumps, to derive the delivery flow rate of the high-density liquid pumphaving a defined displacement volume from the stroke count. In thismeasurement method, the amount of filling of the high-density liquidpump must be estimated. For this reason the result can stronglyfluctuate on the basis of a changing consistency of the high-densityfluid. In order to avoid this problem, it was proposed (DE-A-40 35 515)to determine the amount of filling of the cylinder during each strokewith the help of the most diverse indicators. This method has also beenfound to be too imprecise for many applications, since for thedetermination of the mass flow rate in interest it is necessaryadditionally to determine the density of the material, which causesgreat fluctuations depending upon the consistency of the high-density orthick stock.

SUMMARY OF THE INVENTION

Beginning therewith it is the task of the invention to develop a deviceand a process for determining the delivery rate or the mass flow rate ofthe type described above, with which a precise measurement is possibleeven during fluctuations in the amount of filling of the conveyancecylinder and over a wide ranging variable consistency of the conveyedmaterial.

The inventive solution, in regard to the process aspect, is based on theidea or concept, that the conveyance cylinder is weighed prior to thecarrying out of each fill stroke and prior to the carrying out of eachpressure stroke and from the difference of the weighed value therespective fill amount is determined, and that the cycle time of each ofthe stroke cycles is measured, and that the mathematical computation ofthe delivery rate or the mass flow rate is calculated taking intoconsideration the measured fill amounts.

In order to make this possible it is proposed, with regard to theconstruction aspect, that the conveyance cylinder is provided in ahousing with radial and axial slack and is suspended from at least oneweighing cell provided secured to the housing. The weighing cell makespossible principally in the turn-around phase of the conveyance pistonprior to the carrying out of the filling stroke, and prior to thecarrying out of the pressure stroke, an exact mass determination of theempty and the full conveyance cylinder inclusive of conveyance piston,so that respectively by determination of the difference the fill amountcan be arrived at.

For avoiding the forces which disturb the measurement precision it isproposed, according to a preferred embodiment of the invention, that atleast the part of the conveyance piston guided within the conveyancecylinder is suspended relative to the housing, with radial slack. Thiscan be achieved by suspending the conveyance piston preferablyCardanically from its piston rod with radial slack and/or by elasticallysuspending the conveyance piston or its piston rod with respect to thehousing.

It is envisioned in accordance with a further preferred embodiment ofthe invention that the housing is formed or designed as a round tube orpolygonal tube which surrounds the conveyance cylinder and that on theupper side of the housing two weighing cells are provided in axialseparation from each other. The weighing cells are thereinadvantageously provided on a housing-fixed bearing platform and comprisea spring body armed with a stress or strain measuring strip, while theconveyance cylinder is suspended from the spring body via a carrier rodwhich extends radially through an opening or aperture in the wall of thehousing. The spring body can be formed, for example as a transversebeam, a double transverse beam or shear beam. The aperture through thewall should, for avoidance of an accumulation of dirt which wouldinfluence the measurements, be sealed by a gland seal inserted undertension between the rod and the housing wall.

In order to keep the frictional forces occurring during the weighingprocess as small as possible, it is preferred, when the conveyancecylinder on its charge or in-feed end side is radially slideablysupported by a metallic slide ring which is axially elasticallysupported on the housing. For the same reason the conveyance cylindershould be mounted in the housing with radial slack via an elasticyieldable or deformable quad-ring seal. A further improvement in thisrespect is thereby achieved, when the conveyance cylinder with its driveside end lies with axial slack radially slideably against an abutmentring, and in the area of its drive side end extends through a housingfixed guide jacket with radial slack.

In a two cylinder high density material pump two conveyance cylindersare preferably provided suspended from weighing cells at the housingwith the cylinders provided in a housing with radial and axial slack, ofwhich the conveyance pistons are driven in phase opposition or push pullmanner by hydraulic means.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail byreference to the drawings. There is shown

FIG. 1 a partial break-away perspective representation of a two cylinderhigh density fluid pump;

FIG. 2 a section through a conveyance cylinder of the high density fluidpump according to FIG. 1 hung suspended from a weighing cell;

FIG. 3 a portion of the loading or in-feed end of the conveyancecylinder according to FIG. 2 in enlarged representation.

DETAILED DESCRIPTION OF THE INVENTION

The two cylinder high density fluid pump 10 represented schematically inFIG. 1 is comprised essentially of two conveyance cylinders 12, of whichthe end openings 14 are, via a double helical or worm-gear mixer 16, incommunication with high density fluid material release container 18, andalternatingly have their conveyance piston 20 in communication with adelivery conduit 24 via a branch tube 22 during the pressure stroke, andduring the suction or filling stroke of the respective concernedconveyance piston 20 are in communication with the material releasecontainer 18 for suctioning of material. The conveyance pistons 20 aredriven in opposing phase or push-pull manner via hydraulic drivecylinders 26. Between the drive cylinders 26 and the conveyancecylinders 12 there is found a water box 28 for cleaning the piston rod29 which extends between the drive cylinders 26 and the conveyancecylinders 12.

For determining the delivery rate or the mass flow rate of the materialspumped by the conveyance cylinders 12 to the delivery conduit 24 theconveyance cylinders 12 are mounted floating in a tubular shaped housing30 and suspended from weighing devices 32 provided secured to thehousing. The weighing devices 32 respectively contain a mountingplatform 34 fixed to the housing, a weighing cell 36 comprised of atransverse beam shaped spring body armed with a stress measure strip anda carrier rod 40 with one end mounted on the free end of the transversebeam of the weighing cell 36, extending through hole 38 of the housing30, and with its other end secured to the outer surface of theconveyance cylinder 12. The through hole 38 is, for avoidance ofsoiling, sealed by a bellows seal 39 tensioned between the carrier beam40 and housing 30. The conveyance cylinder 12 is supported at itsloading end 41 radially displaceably on a metallic slide ring 44 whichin turn is supported axially elastically on a seal carrier 42 fixed tothe housing, and via an elastically yieldable quad-ring seal 46 withaxial slack is mounted or supported in the seal carrier 42. On its driveend 46 the conveyance cylinder 12 lies with axial slack radiallyslideable against abutment ring 49 which, for assembly purposes, isremovable and adjustable. Further, the conveyance cylinder 12 extends inthe area of its drive-side end 48 through a housing fixed guide jacket50 with radial slack.

In order to avoid the forces of the conveyance piston 20 acting upon theconveyance cylinder which would interfere with the weighting process,the part of the conveyance piston 20 entering in the conveyance cylinder12 is connected at the connection point 52 with radial slack with itspiston rod 29 guided in a housing fixed guide 54.

With help of the weighing cell 36 it is possible to very preciselydetermine the respective masses of the conveyance cylinder 12 in the twoend positions of the conveyance piston 20, and from the differential ofthe weighing results to calculate the respective fill amount. The thusdetermined fill amounts can, in further consideration of the likewisemeasurable stroke count or stroke frequency, be used for determining themass flow rate through the delivery conduit 24 and for determining thecumulative delivery rate.

In summary the following is to be concluded: The invention concerns adevice and a process for determining the delivery rate or the mass flowrate of a material transported through a delivery conduit 24 by means ofa high-density piston pump 10.

The exact determination of the precise values is made possible thereby,that the conveyance cylinder 12 is provided in the housing 30 withradial and axial slack and is hung up on at least one weighing cell 36provided secured to the housing.

What is claimed is:
 1. A device for determining the delivery rate or themass flow rate of a material conveyed through a delivery conduit (24) bya high-density piston pump (10), the device comprising: at least oneconveyance cylinder (12) having a load end and a drive end; at least oneconveyance piston (20) axially slidable in said conveyance cylinder(12); a housing (30) provided around said at least one conveyancecylinder (12); and at least one weighing cell (36) provided fixed to thehousing; wherein said conveyance cylinder (12) is provided in saidhousing (30) suspended from said weighing cell (36) with radial andaxial slack.
 2. A device according to claim 1, including a piston rodconnected to said conveyance piston (20), wherein at least the part ofthe conveyance piston (20) introduced in the conveyance cylinder (12) issuspended with radial slack relative to the housing (30).
 3. A deviceaccording to claim 2, wherein the piston rod of the conveyance piston(20) is suspended with radial slack.
 4. A device according to claim 3,wherein the piston rod of the conveyance piston (20) is suspendedCardanically.
 5. A device according to claim 2, wherein the conveyancepiston (20) or its piston rod (29) is elastically suspended relative tothe housing (30).
 6. A device according to claim 1, wherein the housing(30) is formed as a round tube or multi-sided tube encompassing saidconveyance cylinder (12).
 7. A device according to claims 1, wherein theconveyance cylinder (12) is oriented horizontally within the housing(30) and wherein two weighing cells (36) are provided on the upper sidethe housing with axial separation from each other.
 8. A device accordingto claim 7, wherein the weighing cells (36) are provided on a mountingplatform (34) fixed to the housing, wherein said weighing cells includea spring body armed with a stress measuring strip, and wherein theconveyance cylinder (12) is suspended from the spring body by a carrierrod (40) which extends through a wall aperture (38) of the housing (30).9. A device according to claim 8, wherein the spring body is formed as atransverse beam, double transverse beam or shear beam.
 10. A deviceaccording to claim 8, wherein the wall aperture (38) is sealed by abellows seal (39) mounted under tension between the carrier rod (40) andthe housing wall (30).
 11. A device according to claim 1, wherein theconveyance cylinder (12) is radially displaceably supported on its loadend (41) on a metallic slide ring (44) which is supported axiallyelastically in the housing (30).
 12. A device according to claim 1,wherein the conveyance cylinder (12) is mounted on the housing (30) withradial slack via an elastic yieldable quad-ring seal (46).
 13. A deviceaccording to claim 1, wherein the conveyance cylinder (12) rests withits drive side end (48) with axial slack radially slideable against anabutment or stop ring (49).
 14. A device according to claim 1, whereinthe conveyance cylinder (12) in the area of its drive end (48) extendswith radial slack through a guide jacket (50) fixed to the housing. 15.A device according to claim 1, wherein two conveyance cylinders (12) areprovided in the housing (30) with radial and axial slack, suspended viaweighing cells (36) in the housing (30), of which the conveyance pistons(20) are driveable in push pull or opposing phase manner by hydraulicmeans (26).
 16. A process for determining the delivery rate or the massflow rate of a material conveyed through a delivery conduit (24) by ahigh-density piston pump (10) comprising at least one conveyancecylinder (12) and conveyance piston (20), wherein during a fillingstroke (suction stroke) the conveyance cylinder is filled with amaterial, for example, from a material providing container, and during apressure stroke, with displacement, the material is emptied into thedelivery conduit (24), wherein the conveyance cylinder (12) is weighedprior to the carrying out of each respective fill stroke and prior tothe carrying out of each respective pressure stroke, that the respectivefill amounts are calculated from the differential in the weight values,and that the cycle time of each respective stroke cycle is measured, andthat by taking into consideration the measured fill amounts themathematical computation of the delivery rate or the mass flow rate iscalculated.